Lymphatic filariasis (LF) is a mosquito-borne Neglected Tropical Disease caused by filarial worms including Brugia malayi; over 120 million people worldwide are infected, with over 1.4 billion at risk in 70 endemic countries. Current control strategies employing mass drug administration have reduced prevalence in many areas, but LF remains a significant global health concern. There is a recognized need for new strategies to control LF and other diseases caused by parasitic nematodes. This project focuses on the host-parasite interface during parasite infection, development and persistence of LF and represents an exciting new direction for investigating this field. We propose a novel mechanism by which B. malayi modulates the host immune system, through small, regulatory RNAs and proteins delivered via a specific type of extracellular vesicle called exosomes. Our preliminary data demonstrate that infective stage larvae of B. malayi secrete exosomes, that these exosomes contain a diverse miRNA and protein cargo and that distinct parasite miRNA potentially target host genes. Further, these exosomes are internalized by host macrophages and elicit a specific modulatory phenotype. The overall goals of this proposal are to define the cargo of parasite exosomes secreted across the intra-mammalian Brugia life cycle and probe the mechanistic basis for their bioactivity. In Specific Aim 1, we propose to profile the small RNA and protein cargo of secreted exosomes across the intra-mammalian B. malayi life cycle using a combination of small RNA deep-sequencing (RNA-Seq) and proteomic profiling to identify the molecular mediators of host manipulation delivered by parasite exosomes. In Specific Aim 2, we will define the mechanisms of exosome bioactivity on cellular mediators of the host immune response. We will examine uptake of parasite exosomes by host macrophages to reveal how these vesicles are internalized by host cells, then leverage the genetic capacity of the murine model by using genetic knock outs to generate mechanistic insight into the modulatory phenotype elicited in host macrophages by exosome internalization. The long-term impact of the project will be new knowledge of B. malayi biology and the exposure of new molecules that may be exploited in novel LF control strategies. Further, the mechanisms we describe here may be conserved across animal, human and plant parasitic nematodes and could be utilized for broad-spectrum control applications.